The invention relates to (alkyl,bromo)phenoxy alkyl(meth)acrylate monomers and polymers made therefrom.
Reactive chemical monomers can be used to prepare polymeric materials which have various properties and which are useful for various applications. As one example, monomers having optical properties can generally be used, alone or in combination with other reactive materials, to produce useful products having a high index of refraction, and that are useful to control the flow and intensity of light. To continually improve such products, or the processes for preparing such products, there is an ongoing need to develop new and improved high index of refraction monomeric materials.
Some brominated aromatic (meth)acrylate monomers have been found to be useful as high index of refraction monomers. These monomers can exhibit desirable optical qualities, but generally tend to display relatively high melting points, and therefore exist as solids at temperatures near room temperature (e.g., in the range from about 20 to 30C). Often such known brominated monomers have melting points significantly above room temperature. In addition, polymerization of these monomers (by themselves or with other comonomers) can frequently lead to a polymer with a relatively high glass transition temperature (Tg) which can limit the range of application of such monomers.
It would be desirable to identify monomers useful to produce optical materials, where the monomers have physical properties including a relatively high index of refraction, a relatively low melting point in combination with a relatively low room temperature viscosity, and which can be used to prepare polymers (e.g., homopolymers or copolymers)having a relatively low Tg.
The invention provides (alkyl,bromo)phenoxy alkyl(meth)acrylate monomers. The term (alkyl,bromo)phenoxy alkyl(meth)acrylate is used herein to refer to chemical compounds comprising a (meth)acrylate, a phenoxy ring substituted with at least bromine and an alkyl group, and a divalent alkylene group connecting the (meth)acrylate to the phenoxy ring. Preferred monomers exhibit a relatively high index of refraction; i.e., at least 1.50. Preferred monomers also have a relatively low melting temperature; i.e., below about 60 degrees celsius (60C), more preferably below about 35C or 30C, and most preferably exist as a liquid at or near normal room temperature (e.g., 25C). In addition, preferred monomers have a relatively low room temperature viscosity, and can be polymerized, either alone or in combination with one or more other comonomers, to prepare polymers with a relatively low glass transition temperature (Tg), e.g.,  less than 50C.
An aspect of the invention relates to (alkyl,bromo)phenoxy alkyl(meth)acrylate monomers such as those having the general formula: 
wherein m is from 1 to 4; R2 is hydrogen or methyl, R1 is a straight or branched alkyl having at least two carbon atoms, and L is a straight or branched alkylene.
Another aspect of the invention relates to a polymerizable composition containing an (alkyl,bromo)phenoxy alkyl(meth)acrylate monomer such as that defined directly above. The polymerizable composition can further contain one or more other comonomer.
Yet another aspect of the invention relates to a polymer or polymeric material comprising a chemical segment having the formula: 
wherein m is from 1 to 4, R2 is xe2x80x94H or methyl, R1 is a straight or branched alkyl having at least two carbons, and L is a straight or branched alkylene. Such a polymer can be prepared by polymerization of the (alkyl,bromo)phenoxy alkyl(meth)acrylate monomer.
As used within the present description, xe2x80x9cmonomerxe2x80x9d refers to a monomer on an individual (i.e., molecular) scale, and also to a composition of such monomers on a macroscopic scale such that the composition can be described as having a physical state of matter (e.g., liquid, solid, etc.) and physical properties (e.g., melting point, viscosity, glass transition temperature (of a polymeric form), and index of refraction).
xe2x80x9cIndex of refraction,xe2x80x9d or xe2x80x9crefractive index,xe2x80x9d refers to the absolute refractive index of a material (e.g., a monomer), which is understood to be the ratio of the speed of electromagnetic radiation in free space to the speed of the radiation in that material, with the radiation being of sodium yellow light at a wavelength of about 583.9 nanometer (nm). Index of refraction can be measured by known methods, and is generally measured using an Abbe Refractometer.
xe2x80x9cGlass transition temperature,xe2x80x9d (Tg), is the temperature range over which a thermoplastic polymer changes from a brittle, glass state to a plastic state. Tg can be measured by methods known in the analytical chemistry art, such as the method described in the Examples section below.
xe2x80x9c(Meth)acrylatexe2x80x9d refers to both acrylate and methacrylate compounds.
Monomers of the invention include (alkyl,bromo)phenoxy alkyl(meth)acrylate monomers, wherein the alkyl group includes at least two carbon atoms (also referred to herein as xe2x80x9cthe monomerxe2x80x9d or xe2x80x9cthe brominated monomer,xe2x80x9d in both singular and plural forms). The (alkyl,bromo)phenoxy alkyl(meth)acrylate monomer can comprise a (meth)acrylate, a phenoxy ring substituted with substituents comprising bromine and an alkyl group, and a divalent alkylene group connecting the two.
The alkyl group can be straight or branched, and can preferably have from 2 to about 12 carbon atoms, more preferably from about 3 to about 12 carbon atoms. The size, position, and structure of the alkyl group are believed to affect properties of the monomer and polymers prepared therefrom, including the refractive index and viscosity of the monomer, and the refractive index and Tg of a polymer made from the monomer. For example, relatively larger or more branched alkyl groups can provide monomers capable of being polymerized to polymers having relatively lower glass transition temperatures, compared to otherwise similar monomers having fewer carbon atoms or less branching. Additionally, a relatively larger alkyl group can result in a monomer or polymer having a relatively lower index of refraction as compared to a similar monomer having a relatively smaller alkyl group.
The alkylene group can generally be any divalent organic hydrocarbon group. The alkylene group can be straight or branched, and preferred alkylene groups can contain from about 1 to about 12 carbon atoms, more preferably from about 2 to about 6 carbons. The size and chemical structure of the alkylene group can affect the physical properties of the monomer and a polymer prepared therefrom, including the refractive index and viscosity of the monomer and the refractive index and Tg of a polymer prepared from the monomer. A relatively larger alkylene group can result in a monomer or polymer having a relatively lower index of refraction as compared to an otherwise similar monomer having a relatively smaller alkylene group. Relatively larger or more branched alkylene groups can provide a monomer which when polymerized has a relatively lower Tg compared to a polymer prepared from otherwise similar monomers having relatively smaller or less branched alkylene groups.
Bromine substitution can affect the index of refraction of the monomer. It is generally understood that bromine increases the index of refraction of the monomer. Bromine can be substituted on the aromatic portion of the monomer in any available amount or position, and will preferably be present in an amount to provide a monomer having a relatively high index of refraction, preferably at least about 1.50. This can be accomplished, for example, by having at least two bromines directly attached to the aromatic ring.
Often, the position of the bromine can be a function of the materials and process used to prepare the brominated monomer (e.g., as described infra). Also, the position of an alkyl group on the aromatic ring can affect at least in part the position of bromines attached directly to the aromatic ring. If an alkyl group is attached at the 4 position relative to the ester substituent (para-), two bromines can preferably be located at the 2 and 6 position, and, if the alkyl group is at the 2 position (ortho-), bromines are preferably at the 4 and 6 positions.
Examples of useful (alkyl,bromo)phenoxy alkyl(meth)acrylate monomers include those having the structure of formula 1: 
wherein:
R2 can be hydrogen (xe2x80x94H) or methyl (xe2x80x94CH3);
m can be from about 1 to 4, and is preferably about 2;
L can be a straight chain or branched alkylene group, preferably containing from 1 to about 12 carbon atoms, more preferably from about 2 to about 6 carbon atoms; and
R1 can be a straight or branched alkyl having at least 2 carbon atoms, preferably having at least 3 and up to about 12 carbon atoms. R1 can be positioned ortho, meta, or para to the phenoxy oxygen.
The monomer preferably exhibits desired properties of index of refraction, melting point, and viscosity. The monomer preferably exhibits an index of refraction of at least about 1.50. The melting point of the monomer can be below about 60C, preferably below about 35C or 30C, and most preferably the monomer exists as a liquid at or near normal room temperature. The monomer can have a room temperature viscosity that allows the monomer or a polymerizable composition thereof to be processed, e.g., pumped, circulated, extruded, coated, formed, cured, or otherwise handled, at or near room temperature. Although viscosities outside of the following ranges can be useful, preferred viscosities of the monomer can be in the range from about 20 to 5000 centipoise (cps), more preferably from about 50 to 1000 cps, as measured at 23C. Also, preferred monomers can be polymerized or copolymerized to provide polymeric materials having relatively low Tg, e.g., below about 50C. Particularly preferred monomers have both a relatively high index of refraction (e.g., greater than about 1.50), and can produce a polymer having a relatively low Tg (e.g., below about 50C).
Examples of useful monomers of the invention include monomers wherein R1 is located ortho to the phenoxy oxygen, as illustrated by formula 2: 
In formula 2, R2, m, L, and R1 are as defined supra. In a particularly preferred embodiment, bromine atoms are located at the 4 and 6 positions on the phenoxy ring, ortho and para to the phenoxy oxygen atom, as illustrated by formula 3: 
Particularly preferred monomers of formula 3 include 4,6-dibromo-2-alkylphenoxy alkylene(meth)acrylates wherein the R1 alkyl has from 3 to 4 carbons, including monomers of the types shown in formulas 4 and 5, wherein R2 and L, are as defined: 
With R2 as hydrogen and L as ethylene these become 2-(4,6dibromo2-sec-butylpenoxy)ethyl acrylate: 
xe2x80x83and 2-(4,6-dibromo-2-isopropylphenoxy)ethyl acrylate: 
With R2 as hydrogen and L as hexylene these become 6-(4,6-dibromo-2-sec-butylpenoxy)hexyl acrylate: 
xe2x80x83and 6-(4,6-dibromo-2-isopropylphenoxy)hexyl acrylate: 
(Alkyl,bromo)phenoxy alkyl(meth)acrylate monomers of the invention can be prepared by methods generally useful in preparing substituted (e.g., brominated) phenoxy compounds and (meth)acrylate monomers. Such methods are well known in the organic chemistry art.
As an example of one method of preparing the monomers of the invention, the following steps can be used. First, an alkyl-substituted phenol(alkylphenol) can be brominated to produce a brominated alkylphenol, as desired to prepare the desired brominated monomer. 
Alkylphenols are commercially available from Schenectady International Inc., Chemical Division, Schenectady, N.Y. Alkylphenols can be brominated by methods that are known in the organic chemistry art, and as described, for example, in the Kirk-Othmer Encyclopedia of Chemical Technology, Volume 4, 543 (4th ed. 1992).
The brominated alkylphenol can be alkylated by known methods to produce an (alkyl,bromo)phenoxy alkanol compound. 
Alkylation methods are known in the chemical art, and are generally accomplished by introducing an alkylating agent, for example any one of an alkylene carbonate (e.g., ethylene carbonate), a chloroalkanol (e.g., chloroethanol) or an alkylene oxide (e.g., ethylene oxide) to the brominated alkylphenol under proper conditions to allow the alkylating agent to react with the phenol alcohol and cause alkylation. See, e.g., U.S. Pat. No. 2,448,767; and Kirk-Othmer, Encyclopedia of Chemical Technology, Vol. 6, 146 (4th ed. 1992).
Also using methods known in the organic chemistry art, the resulting (alkyl,bromo)phenoxy alkanol compound can be esterified to give a brominated (meth)acrylate monomer: 
Esterification reactions are well known in the chemical art, and are described, for example, in the Kirk-Othmer Encyclopedia of Chemical Technology, vol. 1, 291 (4th ed. 1992).
A preferred step in the preparation of the brominated monomer can be a purification step. Purification can be accomplished by any method known in the organic chemistry art, including methods of chromatography and distillation. For some brominated monomers, for example those that might suffer from thermal breakdown at elevated temperatures, it can be preferred to purify the monomers using ultra-high vacuum continuous distillation methods. These processes can be accomplished at pressures in the range from about 1 to 1000 micron mercury (Hg), and temperatures in the range from about 100 to 200C.
The brominated monomer of the invention, alone or in combination with other materials such as other unsaturated polymerizable comonomers, can be included in a polymerizable composition that can be polymerized or co-polymerized to produce useful polymers or copolymers. As used within the present description the term xe2x80x9cpolymerizablexe2x80x9d refers to chemical compounds such as monomers and oligomers, etc., and chemical compositions, capable of polymerizing or copolymerizing (e.g., via unsaturated moieties) to produce a higher molecular weight material such as an oligomer, polymer, prepolymer, or polymeric material. The terms xe2x80x9cpolymerxe2x80x9d and xe2x80x9cpolymeric materialxe2x80x9d are used interchangeably to refer to materials prepared from the reaction of one or more polymerizable materials, e.g., one or more polymerizable monomer, oligomer, polymer, or prepolymer, etc. to produce a dimer, trimer, oligomer, copolymer, homopolymers, etc.
Useful comonomers to be reacted with acrylic monomers such as the brominated monomer described herein are known in the organic chemistry art, and can include any of a number of known and useful polymerizable moieties, e.g., vinyl, (meth)acrylate, N-vinyl, acrylic acid, methacrylic acid, allyl, acrylamide, acrylonitrile, etc. The comonomer can be mono- or multifunctional with respect to the unsaturated moiety, and where multifunctional, the unsaturated moieties need not be of identical chemistry.
Specific types of comonomer useful in the polymerizable composition can include the class of (meth)acrylate-functional comonomers such as butyl(meth)acrylate, as well as vinyl comonomers such as methyl styrene. The particular comonomers included in any given polymerizable composition, their molecular weight or weights, and the included amounts of each, can be chosen according to various factors such as the desired nature and properties of the polymerizable composition and the desired properties of the polymer or polymeric material to be prepared therefrom (e.g., index of refraction, glass transition temperature, melting point, viscosity, etc., of the polymerizable composition or polymeric material).
The polymerizable composition can also contain other ingredients that, as will be appreciated by those skilled in the art of polymeric materials, can be useful in such a polymerizable composition. For example, the polymerizable composition might contain a crosslinking agent, one or more surfactants, pigments, fillers, polymerization inhibitors, or other ingredients that can be useful within a polymerizable composition or an optical product. Such ingredients can be included in the composition in amounts known to be effective for their respective purposes.
A crosslinking agent can be useful to increase the glass transition temperature of the polymer resulting from crosslinking the polymerizable composition. Glass transition temperature of a composition can be measured by methods known in the art, such as Differential Scanning Calorimetry (DSC), modulated DSC QMSC), or Dynamic Mechanical Analysis (DMA).
Polymeric beads, inorganic fillers, and/or pigments can be added to the polymerizable composition in order to improve processing, to impart slip and scratch resistance to the polymerized material, or to affect optical properties of the polymerized material. Examples of useful polymeric beads include those made of polystyrene, polyacrylates, copolymers of styrene and acrylates, polyethylene, polypropylene, polytetrafluoroethylene, or combinations thereof. Examples of inorganic fillers and pigments include solid or hollow glass beads, silica, zirconia, aluminum trihydroxide, and titanium dioxide.
The polymerizable composition can preferably have a room temperature viscosity that allows the polymerizable composition to be processed, e.g., pumped, circulated, extruded, coated, formed, cured, or otherwise handled, at or near room temperature. Although viscosities outside of the following ranges can also be useful, preferred viscosities of the polymerizable composition can be in the range from about 20 to 5000 centipoise (cps), more preferably in the range from about 50 to 1000 cps, as measured at 23C.
Polymerization of the composition can be accomplished by known and usual means, such as heating in the presence of a free-radical initiator, irradiation with electromagnetic radiation such as ultraviolet or visible light in the presence of suitable photoinitiators, and by electron beam. For reasons of convenience and production speed, a preferred method of polymerization might be by irradiation with ultraviolet or visible light in the presence of photoinitiator.